Many tablets today are coated after being pressed. Coating is used to surround or coat a pharmaceutically active ingredient or drug by at least one layer of a surface. Coating is used for recognition, for purposes of masking the taste, or for controlled release purposes to change dissolution properties of active agent. Coating can also been used to work as a barrier against atmospheric stress e.g. humidity, UV-light and oxygen to increase physical and chemical stability of the active agent.
Various methods of coating pharmaceuticals or medical devices are known. Modern tablet coatings are polymer and polysaccharide based, with plasticizers and pigments included. The tablet coating process is complex, and involves parameters such as the spray pattern, drop size, and nozzle spacing, in addition to multiple other non-spray related parameters which must all be precisely controlled in order to ensure uniform distribution of the coating material.
Prior art discloses several methods for coating or encapsulating pharmaceuticals. WO9002546 discloses microencapsulated pharmaceuticals, which are formed by vapor depositing a polymeric film around a core comprising an active pharmaceutical agent to provide effective controlled release activity. DE 10307568 discloses membranes useful in pharmaceutical industry, which have reduced diameter micro- or nanopores produced by coating film with etched or laser produced openings. US 2010/0297251 discloses a method of encapsulating an active pharmaceutical agent with a controlled release coating layer using a gas phase chemical vapor deposition process. The coating materials used are monomers or carbonaceous compounds that upon polymerization yield polymers or polymer films that are degradable or nondegradable. US2009/0186968 discloses atomic plasma deposited coatings over a drug attached to a porous metal substrate. The method is applicable on drugs attached or adhering to a stent surface.
Pharmaceutical industry has a great desire to reduce costs and find new approaches for drug manufacturing and drug delivery. Current approaches of preparing pharmaceutical formulations and pharmaceutical dosage forms are complex, involve a number of technical steps, require special additives or treatments and result in pharmaceutical products with poor stability. In addition, most methods result in low product yields, due, in part, to the limited tolerance of the starting materials to industrial operating conditions and the numerous technical difficulties associated with the coating process. Especially challenging is the dissolution and controlled delivery of poorly soluble pharmaceuticals. Undoubtedly, there is a need for more efficient methods which improve processing techniques and processability of drugs which have poor flow properties and lack of compressibility. Moreover, there remains a need of developing a robust process of preparing pharmaceutical formulations which can be directly processed into the final dosage forms.